(1) Field of the Invention
The present invention relates generally to microstrip patch antennas and, more particularly, to a microstrip patch antenna with a multiband photonic bandgap structure.
(2) Description of the Prior Art
Microstrip patch antennas are very well known.
Microstrip patch antennas consist of thin, flat, printed circuit board antennas. Microstrip patch antennas are relatively inexpensive and easy to manufacture. The radiating elements of the antenna are conducting strips or patches printed on the upper surface of a dielectric substrate that is backed by a conducting ground plate or ground plane. Because such antennas have a very low profile and are mechanically rugged, they are often mounted on exposed exterior surfaces of aircraft and spacecraft, and surfaces such as the periscope of a submarine. They are often incorporated into mobile radio communications devices. These antennas tend to have low backlobes and are not prone to EMI and multipath effects. Microstrip patch antennas are usually employed at UHF and higher frequencies.
In a submarine environment, antenna size is often among the most restrictive of the design requirements. One disadvantage of microstrip patch antennas is that for lower frequencies a relatively large patch size is required. Another disadvantage of microstrip patch antennas is their narrow bandwidth. It has been found that bandwidth can be increased by increasing the substrate thickness. An increase in substrate thickness or dielectric constant can also decrease the resonant patch size. However, increased substrate thickness increases losses due to the substrate and surface waves thus reducing the antenna efficiency. Microstrip patch antennas on high dielectric constant substrates are highly inefficient radiators due to surface wave losses.
The use of photonic band-gap structures of antennas is a relatively new field. It is believed that the concept was first introduced in 1993 in a paper by R. E. Brown, C. D. Parker, and E. Yablon, titled “Radiation Properties of a Planar Antenna on a Photonic-Crystal Substrate.” Much of the work has been on modeling and explaining the photonic bandgap material, rather than actual antenna patterns. Photonic bandgap structures are periodic dielectric structures that prevent propagation of electromagnetic waves in a certain frequency range, i.e, the frequency or wavelength range of the bandgap. Photonic bandgap structure reduces surface wave losses and can significantly increase microstrip patch antenna gain and frequency bandwidth.
The following U.S. patents describe various prior art systems that may be related to the above and/or other telemetry systems:
U.S. Pat. No. 6,518,930, issued Feb. 11, 2003, to Itoh et al, discloses a low-profile cavity-backed slot antenna, including a cavity substrate having a slot with a resonant frequency and a uniplanar compact photonic band-gap (UC-PBG) substrate, proximate to the cavity substrate and having a two-dimensional periodic metallic pattern on a dielectric slab and a ground plane, wherein the UC-PBG substrate behaves substantially as an open boundary at the resonant frequency of the slot. The slot antenna has reduced height while maintaining good performance.
U.S. Pat. No. 6,469,682, issued Oct. 22, 2002, to de Maagt et al, discloses a crystal structure with three-dimensional photonic band gap which comprises a pile of alternate series of layers of distinct dielectric materials having a first and a second determined dielectric constant values, wherein said layers have a constant determined thickness and said pile forms a substantially rectangular parallelepipedal block, and a plurality of parallel channels provided through said block along a direction orthogonal to the main faces of said layers. The channels are distributed according a two-dimensional lattice pattern and have a third determined dielectric constant value. The values for the dielectric constants as well as the relative geometric dimensions of said layers and said channels are selected so as to obtain said three-dimensional photonic band gap in a predetermined frequency range. The crystal structure is especially for use as an antenna substrate.
U.S. Pat. No. 6,177,909, issued Jan. 23, 2001, to Reid et al, discloses a reconfigurable photoconducting antenna that is created on a semiconductor substrate. At equilibrium, the semiconductor is semi-insulating, and therefore appears as a dielectric. Illuminating a region of the substrate results in the generation of free carriers in the substrate and allows the creation of a conductive region (semi-metallic) in the substrate. This conductive region functions as the radiating element of the antenna. Controlling the pattern of the illuminated region directly controls the pattern of the radiating antenna. By using a digital micromirror device to control the pattern of the light, a desired antenna design may be placed on the semiconductor substrate. The pattern can be dynamically adjusted simply by changing the position of the individual mirrors in the array.
The device operates through a standardized digital interface and can be switched between patterns in a period of approximately 20 microseconds. The pattern can therefore be readily and easily controlled through the use of a digital control system.
U.S. Pat. No. 6,175,337, issued Jan. 16, 2001, to Jasper, Jr. et al, discloses a high-gain, dielectric loaded, slotted waveguide antenna having a photonic bandgap, a high-impedance electromagnetic structure, in contact with the waveguide surface containing longitudinal slots, and a tailored dielectric material structure in contact with the outer surface of the photonic bandgap structure. The tailored dielectric structure at the inner most surface has the same effective dielectric constant of the waveguide material and the photonic bandgap structure. The effective dielectric constant is then incrementally or continuously reduced to have a dielectric constant close to that of the free-space value at the outer surface further distance from the waveguide array. The tailoring of the effective dielectric constant is achieved by layering a given number of slabs of different dielectric constants with sequentially reduced values, or by varying the chemical composition of the material, or by varying the density of the material imbedded with high dielectric constant particles.
U.S. Pat. No. 5,689,275, issued Nov. 18, 1997, to Moore et al, discloses a photonic bandgap antenna (PBA) that utilizes a periodic bandgap material (PBM), which is essentially a dielectric, to transmit, receive, or communicate electromagnetic radiation encoded with information. Further, a photonic bandgap transmission line (PBTL) can also be constructed with the PBM. Because the PBA and PBTL do not utilize metal, the PBA and PBTL can be used in harsh environments, such as those characterized by high temperature and/or high pressure, and can be easily built into a dielectric structure such as a building wall or roof. Further, the PBA and PBTL inhibit scattering by incident electromagnetic radiation at frequencies outside those electromagnetic frequencies in the bandgap range associated with the PBM.
The above cited prior art does not disclose a microstrip patch antenna with multiple band photonic bandgap structures. Consequently, those skilled in the art will appreciate the present invention that addresses this problem and other problems.